The present invention relates generally to mechanical fuel pumps. More specifically, the present invention relates to a fuel pump insulator assembly that insulates the fuel pump from engine heat and seals the fuel pump from hot engine oil.
Internal combustion engines using liquid fuels make use of fuel pumps to transfer fuel from fuel storage areas or a fuel tank to the engine's carburetor(s) or fuel injector(s). Fuel pumps are powered electrically or mechanically, with mechanical fuel pumps being powered or driven through being mechanically connected to the engine. Fuel lines connect the fuel tank to the fuel pump, and the fuel pump to the carburetor(s) or injector(s).
Mechanical fuel pumps typically have an enclosed fuel chamber, an inlet valve, an outlet valve, a flexible diaphragm, an arm, and a body on which the fuel chamber is mounted and which provides mounts for the arm. The diaphragm forms a portion of the wall of the fuel chamber, which is otherwise rigid and made of metal or other appropriate material. Fuel enters and exits the fuel chamber through inlet and outlet valves, respectively. The inlet and outlet valves are one-way, with the inlet valve allowing fuel into the chamber but not out, and the outlet valve allowing fuel out of the chamber but not in. Fuel is transferred from the tank to the fuel chamber when the diaphragm is flexed so as to increase the volume of the chamber, creating a pressure differential between the chamber and the tank thus drawing fuel into the chamber. The diaphragm is then flexed in the opposite direction, decreasing the volume of the chamber thereby and forcing fuel out through the outlet valve. The fuel is thus delivered under pressure to the engine. The fuel pump arm is connected to the center of the diaphragm and moves the diaphragm towards and away from the fixed portions of the fuel chamber as it reciprocates. The fuel pump arm rocks on a pivot pin that rotatably passes through pivot holes located perpendicularly to the arm's length, and where the pivot pin has a length longer than the width of the arm and the pivot pin's ends are solidly located in pivot pin mounts which are located inside the pump body cavity. The end of the fuel pump arm located outside the fuel pump body cavity is driven by the engine, typically by the camshaft, in a reciprocating motion which is transferred to the diaphragm as reciprocating motion by virtue of rocking on the pivot pin.
Mechanical fuel pump mounting components generally consist of holes molded or drilled in the fuel pump body through which bolts or studs pass, threading into the engine block or head. The engine block or head is normally machined flat on its exterior surface around the area where the bolts or studs are received, with an opening proximately located allowing the fuel pump arm to extend into the interior of the engine block or head. This area of the engine block or head is known as the engine's fuel pump mounting pad.
The fuel pump arm, passing through the opening in the mounting pad, engages the mechanism internal to the engine block or head which moves the arm in its reciprocating motion. The opening in the mounting pad for the fuel pump arm must be large enough to allow the arm to move through its entire reciprocating motion without interference. Additionally, the opening must be designed to accommodate the installation and removal of the fuel pump, where installation and removal involves the need for the fuel pump arm to be moved vertically, horizontally, and axially as the fuel pump and its arm are moved into their final mounted position around internal and external mechanical obstacles. In some engines, internal actuating mechanism parts must be simultaneously installed with the fuel pump. The opening must also accommodate the end of the arm that contacts the internal mechanism, which is sometimes a machined portion of a flat pad that is larger in cross-section than the rest of the arm. As a result of the considerations just discussed, the mounting pad opening is substantially larger than the external dimensions of the fuel pump arm itself.
The fuel pump body has an ovoid location for the diaphragm and fuel chamber to be mounted. The fuel pump arm pivot mount and ovoid fuel chamber mount are in the interior of the fuel pump body. As discussed above, the fuel pump arm rocks on a pivot pin mounted in a pivot mount in the interior of the fuel pump body, transferring the reciprocating motion from the end of the arm in contact to an internal engine mechanism to the end of the arm inside the fuel pump appended to the diaphragm. The diaphragm has two surfaces, with the surface appended to the fuel pump arm forming part of the fuel pump body internal cavity. The fuel pump body internal cavity, including the surface of the diaphragm appended to the fuel pump arm, forms a contiguous open area with the internal portion of the engine that contains the circulating engine oil when the fuel pump is mounted on an engine.
A gasket is usually fitted between the fuel pump body and the engine mounting pad. The gasket is shaped to fit around the fasteners and around the exterior of the mounting pad opening. The gasket allows heat to be freely transferred from the engine to the fuel pump and only serves to prevent oil leakage at the joint therebetween.
Some manufacturers install a simple insulator between the fuel pump body and the mounting pad when fuel overheating becomes a design concern. Design factors taken into consideration include the fuel pump's location on the engine, where intake and exhaust manifolds are to be located, the location of fuel lines in the engine compartment, where and how the fuel pump and engine assembly is to be mounted for use, and how the engine will actually be used in service. Such an insulator is typically made of a single substance such as fiber or plastic, is flat and relatively thin (usually less than 1/8"), and is cut to a shape that is substantially similar to that of the gasket just discussed, following the outer edge of the mounting pad opening. The insulator is mounted between the mounting pad and the fuel pump body with a gasket or appropriate sealer on each of its flat surfaces. The total thickness of the insulator and gaskets must be kept within specified engineering tolerances to allow the fuel pump arm to properly engage the mechanism which moves the fuel pump arm in a reciprocating motion. The contiguous cavity formed by the inside of the fuel pump body and the inside of the engine is not affected with this type of insulator.
A consequence of using the mounting components and methods described above is that considerable heat is passed into the fuel pump. The heated fuel pump then heats the fuel as the fuel is being pumped, creating numerous problems. As the fuel approaches its vaporization point, it will display highly variable and localized temperature and pressure differentials which cause numerous tuning and running problems. Power drops off, fuel consumption rises, emissions rise, and the engine runs roughly. As the fuel temperature continues to rise, engine performance degrades until the fuel vaporizes, causing vapor lock. The engine will then stop running and can be very difficult to restart as the fuel pump and the surrounding fuel lines must cool to the point where the fuel again becomes liquid, often involving a significant wait.
There are three primary ways in which heat is passed to the fuel pump assembly when the mounting components and methods discussed above are used to mount a mechanical fuel pump. One is through the mounting pad when a standard insulator is not used, one is from the mounting pad through the mounting fasteners to the fuel pump body, and one is from hot engine oil impinging directly into the interior of the fuel pump body and onto the diaphragm. When using the currently available insulator with gaskets or sealers, heat continues to be transferred to the fuel pump body from the mounting pad through the mounting fasteners and from hot engine oil contacting the interior of the fuel pump body and the diaphragm. Use of the industry standard insulator somewhat reduces the frequency with which vapor lock occurs, and somewhat increases the temperature at which the engine and can operate without vaporizing the fuel. However, with the continued direct exposure of the fuel pump body to the hot engine oil and the heat coming through the mounting fasteners, the protection offered by the standard insulator against heating and vaporization is not enough in hot climates nor under heavy use. In racing applications the standard insulator is inadequate, where it is normal for racing vehicles to experience rough running and power loss due to fuel overheating and to stall and experience difficulty restarting due to vaporization.